1. Field of the Invention
The present invention relates generally to article handling and conveying and, more particularly, to equipment for unloading dairy product containers from a truck trailer and depositing them onto a conveyor system.
2. The Prior Art
In accordance with the usual practice, plastic milk bottles or containers are hand-packed into large bags at the manufacturing plant. The containers are stacked within the bag, requiring a center board and at least one piece of corrugated packing for protecting the containers against damage. After packing, the bags are sealed with wire ties or by heat sealing equipment. Containers packaged in this manner are then stacked on pallets, which are then loaded into truck trailers for subsequent delivery to the dairy. At the dairy, the bags containing the bottles must be manually unloaded from the truck trailer, transported by forklift, and then manually opened. The bottles are removed from their bags and placed one-by-one on a conveyor system leading to a filling line. Recently, plastic containers, specifically the type which are blow molded, have been found to be acceptable alternatives to glass bottles and paper cartons for packaging milk. However, expenditures in man-power and product time required by the aforementioned method of manually packaging and unloading the containers for transport to the dairy filling line have kept the cost of using plastic containers undesirably high.
The above-identified U.S. Ser. No. 111,019 discloses an automatic system by which articles, such as plastic dairy containers, transported in a truck trailer may be unloaded and deposited onto a conveyor system. By providing apparatus capable of rapid and automatic unloading of plastic containers, the effective cost of plastic containers can be meaningfully reduced and the resulting product is quite cost competitive with paper and glass packaging. The automatic system includes an article unloader section in which articles are removed from carrier racks by means of a push rod assembly. The articles are arranged in the carrier on a series of shelves in which rows of bottles are aligned behind a line of forwardmost bottles. The push rod assembly serves to push the carrier bottles a forwardmost line at a time onto respective platforms of a article elevator, which passes the articles upward to adjacent a transfer mechanism. The transfer mechanism drives a set of lift fingers about a circular path which at one point intermesh with each elevator platform laden with articles to pick the articles up and transfer them onto a stationary shelf with which the finger set coincides further along its path. Paddles formed on an endless belt intermediate conveyor push the line of articles out onto a conveyor system which, in the case of dairy bottles, may lead to the dairy filling line. The elevator, transfer mechanism, and intermediate conveyor drives are all correlated to a common drive motor positioned at the lower end of the elevator in direct drive relationship with the lower elevator sprocket shaft. Drive transmission means for the correlated unloader elements are heavily made up of chains. Chains inherently have slack and, after a period of time, these chains stretch so that more slack is created in the lines. As movement of counterweights secured to drive shafts for the transfer mechanism shifts the tension on the elevator drive chain, relative movement slippage occurs. The result of this slippage is a jerking motion of the transfer mechanism tending to throw articles from the fingers. After a period of time, the lift fingers and elevator platforms move out of synchronization with one another, resulting in many articles coming ajar and not reaching the conveyor system and, especially in the case of the plastic containers, many articles being crushed, punctured, or otherwise destroyed.
Further problems occurring in the unloader operation for the automatic system disclosed in U.S. Ser. No. 111,019 arise in that, when lightweight plastic containers are being handled, stable supports and proper positioning of the containers becomes critical because the containers are so easily toppled. The present invention overcomes the aforementioned problems in the automatic unloading system, resulting in less downtime for the system and more reliable automatic unloading.